MIT Breakthrough Makes Carbon Capture 6x More Efficient

MIT researchers have developed a powerful improvement to carbon capture tech by using nanofiltration membranes to separate key chemical ions, drastically enhancing efficiency and stability.

This clever middle step allows both capture and release phases to run more effectively, potentially cutting costs by 20% and making the process more forgiving to fluctuations. The system is not only compatible with existing infrastructure but could also pave the way for safer, greener chemistry in carbon management.

The Challenge of Efficient Carbon Capture

Removing carbon dioxide from the atmosphere is widely considered one of the most important tools for fighting climate change. But there’s a frustrating catch: the chemicals that are best at pulling CO₂ out of the air tend to cling to it too tightly, making it hard to release later. On the flip side, compounds that let go of CO₂ easily aren’t great at capturing it in the first place. It’s a balancing act, and improving one part usually means weakening the other.

Now, researchers at MIT have found a clever way to overcome this challenge. By adding a nanoscale filtering step in the middle of the carbon capture process, they’ve managed to boost efficiency by a factor of six, while also lowering costs by at least 20 percent. This innovation could make carbon removal significantly more practical and scalable.

The work, published in ACS Energy Letters, comes from a team including MIT doctoral students Simon Rufer, Tal Joseph, and Zara Aamer, along with mechanical engineering professor Kripa Varanasi.

Thinking Big From the Start

“We need to think about scale from the get-go when it comes to carbon capture, as making a meaningful impact requires processing gigatons of CO₂,” says Varanasi. “Having this mindset helps us pinpoint critical bottlenecks and design innovative solutions with real potential for impact. That’s the driving force behind our work.”

Traditional systems often use a chemical called hydroxide, which quickly reacts with carbon dioxide in the air to form carbonate. That carbonate is then sent into an electrochemical cell, where it reacts with acid, turning into water and releasing pure CO₂. The result is a clean, concentrated stream of carbon dioxide that can be reused for making fuel or other valuable products.

However, there’s a major hitch. Both the capture and release stages happen in the same water-based liquid. The capture step works best in a liquid full of hydroxide ions, while the release step needs that liquid to contain mostly carbonate ions.

“You can see how these two steps are at odds,” says Varanasi. “These two systems are circulating the same sorbent back and forth. They’re operating on the exact same liquid. But because they need two different types of liquids to operate optimally, it’s impossible to operate both systems at their most efficient points.”

A Smart Three-Part System

The team’s solution was to decouple the two parts of the system and introduce a third part in between. Essentially, after the hydroxide in the first step has been mostly chemically converted to carbonate, special nanofiltration membranes then separate ions in the solution based on their charge. Carbonate ions have a charge of 2, while hydroxide ions have a charge of 1. “The nanofiltration is able to separate these two pretty well,” Rufer says.

Once separated, the hydroxide ions are fed back to the absorption side of the system, while the carbonates are sent ahead to the electrochemical release stage. That way, both ends of the system can operate at their more efficient ranges. Varanasi explains that in the electrochemical release step, protons are being added to the carbonate to cause the conversion to carbon dioxide and water, but if hydroxide ions are also present, the protons will react with those ions instead, producing just water.

“If you don’t separate these hydroxides and carbonates,” Rufer says, “the way the system fails is you’ll add protons to hydroxide instead of carbonate, and so you’ll just be making water rather than extracting carbon dioxide. That’s where the efficiency is lost. Using nanofiltration to prevent this was something that we aren’t aware of anyone proposing before.”

Demonstrating Real-World Viability

Testing showed that the nanofiltration could separate the carbonate from the hydroxide solution with about 95 percent efficiency, validating the concept under realistic conditions, Rufer says. The next step was to assess how much of an effect this would have on the overall efficiency and economics of the process. They created a techno-economic model, incorporating electrochemical efficiency, voltage, absorption rate, capital costs, nanofiltration efficiency, and other factors.

The analysis showed that present systems cost at least $600 per ton of carbon dioxide captured, while with the nanofiltration component added, that drops to about $450 a ton. What’s more, the new system is much more stable, continuing to operate at high efficiency even under variations in the ion concentrations in the solution. “In the old system without nanofiltration, you’re sort of operating on a knife’s edge,” Rufer says; if the concentration varies even slightly in one direction or the other, efficiency drops off drastically. “But with our nanofiltration system, it kind of acts as a buffer where it becomes a lot more forgiving. You have a much broader operational regime, and you can achieve significantly lower costs.”

Beyond Direct Air Capture

He adds that this approach could apply not only to the direct air capture systems they studied specifically, but also to point-source systems — which are attached directly to the emissions sources such as power plant emissions — or to the next stage of the process, converting captured carbon dioxide into useful products such as fuel or chemical feedstocks. Those conversion processes, he says, “are also bottlenecked in this carbonate and hydroxide tradeoff.”

In addition, this technology could lead to safer alternative chemistries for carbon capture, Varanasi says. “A lot of these absorbents can at times be toxic, or damaging to the environment. By using a system like ours, you can improve the reaction rate, so you can choose chemistries that might not have the best absorption rate initially but can be improved to enable safety.”

Ready for Real-World Use

Varanasi adds that “the really nice thing about this is we’ve been able to do this with what’s commercially available,” and with a system that can easily be retrofitted to existing carbon-capture installations. If the costs can be further brought down to about $200 a ton, it could be viable for widespread adoption. With ongoing work, he says, “we’re confident that we’ll have something that can become economically viable” and that will ultimately produce valuable, saleable products.

Rufer notes that even today, “people are buying carbon credits at a cost of over $500 per ton. So, at this cost we’re projecting, it is already commercially viable in that there are some buyers who are willing to pay that price.” But by bringing the price down further, that should increase the number of buyers who would consider buying the credit, he says. “It’s just a question of how widespread we can make it.” Recognizing this growing market demand, Varanasi says, “Our goal is to provide industry-scale, cost-effective, and reliable technologies and systems that enable them to directly meet their decarbonization targets.”

Reference: “Carbonate/Hydroxide Separation Boosts CO₂ Absorption Rate and Electrochemical Release Efficiency” by Simon Rufer, Tal Joseph, Zara Aamer and Kripa K. Varanasi, 20 May 2025, ACS Energy Letters.
DOI: 10.1021/acsenergylett.5c00893

The research was supported by Shell International Exploration and Production Inc. through the MIT Energy Initiative, and the U.S. National Science Foundation, and made use of the facilities at MIT.nano.

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